JP2006211040A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device which is a circularly-polarized wave slot antenna of a one-point power feeding system and can be easily miniaturized. <P>SOLUTION: A radiation slot 3 formed at a metallic flat plate 2 is composed of a main slot 6 located on one diagonal line of the metallic flat plate 2 and first and second branch slots 7, 8 extended along two adjacent sides of the metallic flat plate 2. A feeding line 4 and a ground line 5 are arranged near one end of the main slot 6. The other end of the main slot 6 is made to communicate with the first branch slot 7. The vicinity of the other end of the main slot 6 is branched and made to communicate with the second branch slot 8. The length and the relative position of each slot 6-8 are set so that a polarization plane of a radio wave emitted from the slots 6, 7 and that of a radio wave emitted from the slots 6, 8 are orthogonal to each other, and also, a phase difference of 90° is generated between the former radio wave and the latter radio wave. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an antenna device having a slot antenna structure, and more particularly to an antenna device suitable as a small circularly polarized antenna.

  As a circularly polarized antenna having a slot antenna structure, conventionally, a pair of radiating slots of the same length and spatially orthogonal to each other are fed and excited, and a position of 90 degrees is placed between radio waves radiated from each radiating slot. A two-point feeding type antenna device in which a phase difference is generated is common. However, the two-point power feeding method that requires a 90-degree phase difference circuit or the like has a problem that the circuit configuration becomes complicated.

Therefore, recently, an L-shaped radiating slot formed by communicating one end of the first slot portion and the second slot portion that are spatially orthogonal to each other is provided in the conductor plate, and power is supplied to an appropriate position near the corner portion of the radiating slot. Thus, there has been proposed a one-point feeding type antenna device in which a phase difference of 90 degrees is generated between radio waves radiated from each slot (see, for example, Patent Document 1).
JP 2004-194218 A (page 6, FIG. 7)

  The above-described conventional antenna device has an advantage that the circuit configuration can be simplified because it is a single-point feeding type circularly polarized antenna. However, when the wavelength of the radio wave to be used is λ, the first slot portion and the second slot portion Since the total length of each is about λ / 2, the conductor plate that opens the L-shaped radiation slot needs to have a size of one side λ / 2 or more. Accordingly, when the operating frequency is, for example, 2.4 GHz, this antenna device requires a size of 6 cm or more on the side of the conductor plate that opens the L-shaped radiation slot, and the desired size reduction cannot be achieved. there were.

  The present invention has been made in view of the actual situation of the prior art, and an object of the present invention is to provide an antenna device that is a single-point-feed type circularly polarized slot antenna and that is easily reduced in size. .

  In order to achieve the above object, in the antenna device of the present invention, a radiation slot provided in a conductor member extends in a straight line and has a main slot portion having a power feeding portion in the vicinity of one end portion, and sandwiches the main slot portion. The first branch slot portion and the second branch slot portion are provided in regions opposite to each other and extend linearly, and the first branch slot portion is provided at the other end of the main slot portion. The second branch slot portion is communicated with the vicinity of the other end portion, and the polarization plane of the radio wave radiated from the main slot portion and the first branch slot portion, the main slot portion and the second slot Each so that the plane of polarization of the radio wave radiated from the branch slot part is orthogonal, and a phase difference of 90 degrees occurs between the former radio wave and the latter radio wave. Set the length and relative position of the lot unit.

  The radiation slot of the antenna device configured as described above includes a first V-shaped slot extending from the main slot portion to the first branch slot portion, and a second V-shape extending from the main slot portion to the second branch slot portion. The radio wave radiated from the first V-shaped slot and the radio wave radiated from the second V-shaped slot have a plane of polarization orthogonal to each other and 90 degrees. Since the phase difference is maintained, circularly polarized waves with good axial ratio characteristics can be radiated if the amplitudes of both radio waves are set to the same level. That is, this antenna device can be operated as a single-point feed circularly polarized slot antenna with a simple configuration. Further, in this antenna device, when the wavelength of the radio wave to be used is λ, the sum of the total length of the main slot portion and the first branch slot portion (or the second branch slot portion) is set to about λ / 2. Since it is good, a radiation slot can be opened in a small-sized conductor member whose one side is sufficiently shorter than λ / 2, which facilitates miniaturization.

  In the above configuration, if the total length of the second branch slot portion is less than or equal to the total length of the first branch slot portion, the total length of the second V-shaped slot is slightly shorter than the total length of the first V-shaped slot. Thus, a phase difference of 90 degrees can be caused by this difference in length.

  In the above configuration, an angle formed between the main slot portion and the first branch slot portion is approximately 45 degrees, and an angle formed between the main slot portion and the second branch slot portion is approximately 45 degrees. In this case, since the angle formed by the first branch slot portion and the second branch slot portion located in areas opposite to each other across the main slot portion is approximately 90 degrees, each slot portion is disposed in a compact manner. This is preferable. In this case, if the outer shape of the conductor member is substantially square in plan view, the main slot portion is provided on one diagonal line of the substantially square so that the first and second sides along two adjacent sides of the substantially square are provided. Since the branch slot portion can be provided, an antenna device having a good space factor and suitable for downsizing can be obtained.

  In the above configuration, the conductor member may be a metal plate or a metal film. However, when the conductor member is made of a metal plate, the antenna device can be formed only by sheet metal. Therefore, the manufacturing cost can be significantly reduced.

  In addition, when the conductor member is made of a metal film formed on a dielectric substrate, it is possible to promote downsizing of the entire apparatus due to the wavelength shortening effect by the dielectric.

  According to the antenna device of the present invention, the radio wave radiated from the main slot portion and the first branch slot portion and the main slot portion are appropriately selected by appropriately selecting the length and relative position of each slot portion of the radiation slot opened in the conductor member. And the radio wave radiated from the second branch slot portion is set so as to generate a phase difference of 90 degrees while the planes of polarization are orthogonal to each other. it can. In addition, the antenna device may be set to a half of the wavelength of the radio wave using the sum of the total length of the main slot portion and the total length of the first branch slot portion (or the second branch slot portion), so that a conductor with a small area Radiation slots can be opened in the member, which facilitates miniaturization.

  An embodiment of the invention will be described with reference to the drawings. FIG. 1 is a perspective view of an antenna device according to a first embodiment of the present invention, FIG. 2 is a plan view of the antenna device, and FIG. FIG. 4 is a characteristic diagram showing a radiation pattern of the antenna device.

  The antenna device shown in FIGS. 1 and 2 includes a box-shaped metal case 1 made of a metal plate 2 having a square top plate portion, a radiation slot 3 provided in the metal plate 2, and a feeding position of the radiation slot 3. The power supply line 4 and the ground line 5 that extend downward are schematically configured, and the radiation slot 3 is formed in a shape in which three slot portions 6, 7, 8 that extend in a straight line are communicated.

  The metal case 1 is obtained by pressing a sheet metal, and is formed into a box shape by bending the four side plate portions 1a extending from each side of the metal flat plate 2 downward. The metal case 1 is placed on a circuit board (not shown) provided with a high-frequency circuit such as a power feeding circuit.

  The radiating slot 3 is formed by punching the metal flat plate 2 into a predetermined shape, and is positioned in a region opposite to each other across the main slot 6 located on one diagonal line of the metal flat plate 2 and the main slot 6. The metal plate 2 includes a first branch slot portion 7 and a second branch slot portion 8 extending along two adjacent sides. In the vicinity of one end of the main slot 6, a feed line 4 and a ground line 5 are disposed with the slot 6 interposed therebetween. The other end portion of the main slot portion 6 communicates with one end portion of the first branch slot portion 7, and the angle formed by both the slot portions 6 and 7 is set to 45 degrees. Further, the vicinity of the other end portion of the main slot portion 6 branches and communicates with one end portion of the second branch slot portion 8, and the angle formed by both the slot portions 6 and 8 is set to 45 degrees. The overall length of the main slot portion 6 is approximately √2 times the overall length of the first branch slot portion 7, and the overall length of the second branch slot portion 8 is formed to be equal to or slightly shorter than the overall length of the first branch slot portion 7. By doing so, the total length of the first V-shaped slot extending from the main slot portion 6 to the first branch slot portion 7 and the second V-shaped slot extending from the main slot portion 6 to the second branch slot portion 8 are achieved. The total length is slightly different. However, this difference in length is slight, and the total length of each V-shaped slot is set to about half the wavelength λ of the radio wave used.

  The radiation slot 3 can be regarded as a superposition of the first V-shaped slot formed of the slot portions 6 and 7 and the second V-shaped slot formed of the slot portions 6 and 8. Then, by appropriately selecting the length, relative position, power supply position, and the like of each of the slot portions 6, 7, and 8, it is set to generate an electric field as indicated by a vector in FIG. 2 during excitation. That is, in the figure, Ea represents an electric field generated in the main slot section 6, Eb represents an electric field generated in the first branch slot section 7, Ec represents an electric field generated in the second branch slot section 8, and Ea / 2 The combined vector of Eb and Eb becomes the electric field E1 of the first V-shaped slot, and the combined vector of Ea / 2 and Ec becomes the electric field E2 of the second V-shaped slot. As shown in FIG. 2, the directions of the electric field E1 and the electric field E2 are orthogonal to each other, and the magnitudes of the electric field E1 and the electric field E2 are substantially equal. In addition, since the first V-shaped slot and the second V-shaped slot have different total lengths, the electric field E1 and the electric field E2 are out of phase, but each V-shaped slot has a phase difference of 90 degrees. The total length is set.

  As shown in FIG. 1, the feed line 4 and the ground line 5 are formed by bending the extending portion of the metal flat plate 2 downward with two bases sandwiching the vicinity of one end of the main slot 6 in the width direction. The lower ends of both metal pieces are soldered to the circuit board. That is, the lower end of the feed line 4 is connected to the feed circuit, and the lower end of the ground line 5 is connected to the ground.

  The antenna device configured as described above feeds power to the radiation slot 3, whereby the first V-shaped slot including the main slot portion 6 and the first branch slot portion 7, the main slot portion 6, and the second slot. The second V-shaped slot formed of the branch slot portion 8 can be excited simultaneously. The radio wave radiated from the first V-shaped slot (electric field E1) and the radio wave radiated from the second V-shaped slot (electric field E2) have a polarization plane orthogonal to each other and a phase difference of 90 degrees. And the radiating slots 3 radiate circularly polarized waves as a whole. That is, this antenna device operates as a single-point feed circularly polarized slot antenna with a simple configuration.

  Note that the return loss (S11) corresponding to the frequency of the antenna device changes as shown in FIG. In the figure, f1 indicates the resonance frequency of the first V-shaped slot, and f2 indicates the resonance frequency of the second V-shaped slot. Further, when the XYZ axes are defined as shown in FIG. 1, the radiation pattern of the YZ plane of this antenna device is as shown in FIG. 4A, and the radiation pattern of the XZ plane is as shown in FIG. 4B. . However, in FIG. 4, the curve indicated by the solid line indicates left-handed circularly polarized wave (LHCP), and the curve indicated by a broken line indicates right-handed circularly polarized wave (RHCP). As is clear from FIG. 4, this antenna device has a high gain of circularly polarized waves (in this case, left-handed circularly polarized waves) in a wide angle range in the zenith direction of the metal flat plate 2, and a user-friendly radiation pattern can be obtained.

  Further, in this antenna device, the radiation slot 3 is compactly opened on the square metal plate 2, and when the wavelength of the radio wave used is λ, the total length of each V-shaped slot is set to about λ / 2. Therefore, the length of one side of the metal flat plate 2 may be about λ / 3. Therefore, when the operating frequency is in the 2.2 GHz band, for example, the antenna device can open the radiation slot 3 in the metal flat plate 2 having a side of about 4.5 cm, and the miniaturization is easily promoted. When this antenna device is applied to wireless communication with an operating frequency of 2.4 GHz, the radiation slot 3 can be opened in the metal flat plate 2 having a side of about 4.2 cm, and the ETC (operating frequency is 5.8 GHz). When applied to an automatic toll collection system), the radiation slot 3 can be opened on the metal flat plate 2 having a side of about 1.7 cm.

  Further, in this antenna device, since the feed line 4 and the ground line 5 made of a metal piece extending from the metal flat plate 2 are used as the feed means for the radiation slot 3, the entire antenna device including the feed means is only made of sheet metal. Can be formed. Therefore, this antenna device can be manufactured at a very low cost.

  FIG. 5 is a plan view of an antenna device according to a second embodiment of the present invention, and FIG. 6 is a characteristic diagram showing an axial ratio pattern of the antenna device. In FIG. 5, parts corresponding to those in FIG.

  The antenna device shown in FIG. 5 is provided with a wide portion 9 at a communication location of the main slot portion 6 and the first branch slot portion 7 to increase the current flowing to the branch slot portion 7 side, thereby increasing the second branch slot portion 8. It is configured so that a relatively large amount of current does not flow to the side. That is, since the first V-shaped slot formed of the main slot portion 6 and the first branch slot portion 7 is slightly longer than the second V-shaped slot formed of the main slot portion 6 and the second branch slot portion 8, the impedance is reduced. Due to the difference, the current flows more easily into the second V-shaped slot than in the first V-shaped slot, in which case the electric field E1 of the first V-shaped slot is less than the electric field E2 of the second V-shaped slot. There is a possibility that the axial ratio characteristic is deteriorated as desired. Therefore, in this embodiment, the wide portion 9 is provided in the radiation slot 3 to facilitate the flow of current to the first branch slot portion 7 side, so that substantially the same amount of current flows in the branch slot portions 7 and 8. Therefore, the magnitudes of the electric field E1 and the electric field E2 are made equal. As a result, this antenna device had a good axial ratio pattern as shown in FIG. In FIG. 6, the curve indicated by the solid line is the XZ plane axial ratio pattern, and the curve indicated by the broken line is the YZ plane axial ratio pattern.

  FIG. 7 is a plan view of the antenna device according to the third embodiment of the present invention. The same reference numerals are given to the portions corresponding to those in FIG. 2 and FIG.

  The antenna device shown in FIG. 7 is greatly different from the first and second embodiments described above in that the radiation slot 3 is opened in the metal film 11 on the dielectric substrate 10 instead of the metal plate. The metal film 11 is connected to a ground (not shown) via a plurality of via holes 12, and is provided with a notch 13 that narrows the communication point between the main slot 6 and the second branch slot 8. .

  The antenna device configured in this way can be further miniaturized due to the wavelength shortening effect by the dielectric, and the notch 13 narrows the communication portion of the main slot 6 and the second branch slot 8. Since the current flowing toward the branch slot portion 8 is reduced, the axial ratio characteristics can be improved by allowing substantially the same amount of current to flow through the branch slot portions 7 and 8.

1 is a perspective view of an antenna device according to a first embodiment of the present invention. It is a top view of the antenna device. It is a characteristic view which shows the return loss of this antenna apparatus. It is a characteristic view which shows the radiation pattern of this antenna apparatus. It is a top view of the antenna apparatus which concerns on the 2nd Example of this invention. It is a characteristic view which shows the axial ratio pattern of this antenna apparatus. It is a top view of the antenna device which concerns on the example of 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal case 2 Metal flat plate 3 Radiation slot 4 Feeding line 5 Grounding line 6 Main slot part 7 1st branch slot part 8 2nd branch slot part 9 Wide part 10 Dielectric substrate 11 Metal film 13 Notch part

Claims (6)

Radiation slots provided in the conductor member extend in a straight line and are provided in a main slot part having a power feeding part in the vicinity of one end part and areas opposite to each other across the main slot part, and each extend in a straight line. A first branch slot portion and a second branch slot portion, wherein the first branch slot portion communicates with the other end portion of the main slot portion, and the second branch slot portion is located near the other end portion. Communicated,
The polarization plane of the radio wave radiated from the main slot portion and the first branch slot portion is orthogonal to the polarization plane of the radio wave radiated from the main slot portion and the second branch slot portion, and the former radio wave. An antenna device characterized in that the length and relative position of each slot portion are set so that a phase difference of 90 degrees is generated between the first and second radio waves.   2. The antenna device according to claim 1, wherein an overall length of the second branch slot portion is equal to or less than an overall length of the first branch slot portion.   The angle formed between the main slot portion and the first branch slot portion is approximately 45 degrees, and the angle formed between the main slot portion and the second branch slot portion is substantially set forth in claim 1 or 2. An antenna device characterized by being 45 degrees.   4. The antenna device according to claim 3, wherein an outer shape of the conductor member is a substantially square in plan view, and the main slot portion is provided on one diagonal line of the substantially square.   The antenna device according to any one of claims 1 to 4, wherein the conductor member is made of a metal plate.   5. The antenna device according to claim 1, wherein the conductor member is made of a metal film formed on a dielectric substrate.

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